A significant percent of the human population develops an ocular refractive error requiring correction by glasses, contact lenses, or surgical procedures. Refractive errors result when the optical elements of the eye, the cornea and the lens, fail to image light directly on the retina. If the image is focused in front of the retina, myopia or nearsightedness exists; whereas, an eye which focuses images behind the retina is said to be hyperopic or farsighted. Furthermore, an eye which has power that varies significantly in different meridians is said to be astigmatic. The focusing power of the eye is measured in units called diopters, and the cornea is responsible for about two-thirds of the eye's sixty diopter refracting power with the lens contributing the remainder.
In addition to corrective lenses, that is glasses, contact lenses and inter-ocular lenses, opthalmologists have derived a number of surgical procedures which attempt to correct refractive errors. These involve various forms of profiling of the cornea. Example procedures of those as heretofore proposed are discussed in U.S. Pat. No. 5,423,801, No. 5,133,708, No. 5,196,027, and others, and the patents and articles cited therein. U.S. Pat. No. 5,423,801 describes a procedure for re-profiling the Bowman's membrane of the cornea of the eye, and in particular controlling laser radiation so that ablation terminates substantially within Bowman's membrane and not the underlying stroma. The re-profiling technique is for ablation and reshaping the cornea to change the profile or curvature thereof.
In addition to these surgical techniques, variable power optical lenses are widely used for correcting aberrations of the eye. One inter-ocular lens providing multifocal capabilities is described in U.S. Pat. No. 5,158,572. According to this patent, a multifocal lens can be formed having a substantially circular central region having a first optical power, surrounded by a plurality of concentric ring regions having at least two optical powers, one of which may be the first optical power.